The present invention relates to a magnetization drive method, a magnetic functional device, and a magnetic apparatus, which are typically suitable to be used for solid-state magnetic memories.
As compared with semiconductor devices, magnetic devices using magnetic substances have the following merits. First, since components of a magnetic device can be made from metals having high carrier densities and low resistances, such a magnetic device may be suitable for realizing a very fine-structure of the magnetic device, such as a structure having sub-micron dimensions. Second, since a magnetic substance exhibits bi-stable magnetization directions, the magnetization state of the magnetic substance can be stably kept even when external energy is not given to the magnetic substance, with a result that such a magnetic substance is suitable for realizing a non-volatile memory function. Third, if a magnetic field having a sufficient strength is applied externally to a magnetic substance of a magnetic device, a magnetization direction of the magnetic substance can be changed into the field direction for a time being as short as about 1 ns, and accordingly, the magnetic device can realize very fast switching of the magnetization direction.
Magnetic devices using magnetic substances, which have the above-described merits, may be applied to high integration solid-stage memories operated at high speeds to realize energy-saving.
However, the benefit associated with high speed operation of magnetic devices tends to be lost along with the progress of the degree of fineness of fine-structures of the magnetic devices due to the following causes:
One of the causes is that, as described in the earlier application by the present applicant, Japanese Patent Laid-open No. Hei 10-130711, as wires become thinner along with the progress of fineness of a finer-structure of a magnetic device, the amount of a current flowing through the wires tends to be restricted, thereby making it impossible to generate a magnetic field having a sufficient strength. The stronger the magnetic field applied to the magnetic device, the faster the magnetization switching speed thereof. Accordingly, the restriction of the applied magnetic field limits the switching speed of the magnetic device.
Another cause is that as the size of a magnetic substance whose magnetization direction is to be switched becomes small, a damping force applied to damp the movement of a magnetization vector of the magnetic substance becomes small. If the damping force becomes excessively small, the magnetization vector continuously rounds around the field direction, with a result that it takes a lot of time for the magnetization vector to be converged in the field direction.
The reason why the damping force applied to damp the movement of a magnetization vector of a magnetic substance becomes small with a reduction in size of the magnetic substance will be described below. In a magnetic metal thin film used for a solid-state magnetic memory such as a magnetic random access memory (MRAM), during movement of magnetization, an eddy current flow in the direction in which the eddy current obstructs the movement of the magnetization. A Joule heat generated by the eddy current is the dominant part of the loss in movement of magnetization. An eddy current loss density per volume, p(W/m3) is approximately proportional to the cross-section of the magnetic thin film, that is, a magnetic substance. That is to say, as the size of a magnetic substance becomes small, the strength of a damping force applied to damp a magnetization vector of the magnetic substance becomes small approximately in proportion to the square of the size of the magnetic substance.
An object of the present invention is to provide a magnetic functional device including a magnetic substance, which allows magnetization switching at a high speed even if the size of the magnetic substance is made finer on the sub-micron order, a magnetization drive method for the magnetic functional device, and a magnetic apparatus using the magnetic functional device.
First, a general theory concerned with the movement of a magnetization vector will be described.
An equation of a magnetic moment is given, for example, by Landau and Lifshits as follows:
dM/dt=xe2x88x92xcex3xc2x7(Mxc3x97H)xe2x88x92(xcex1xc2x7xcex3/Ms)xc2x7{Mxc3x97(Mxc3x97H)}xe2x80x83xe2x80x83(1)
where M is a magnetization vector, H is a vector of a magnetic field, xcex3 is a gyromagnetic constant, and a is xcex1 damping factor. If xcex1 is significantly larger than 1, the magnetization vector is slowly converged to the direction of an external magnetic field. For example, when a magnetic field in the xe2x88x92x direction is applied to a magnetization vector directed nearly in the +x direction within an xy plane, if the damping is large, the magnetization vector slowly rounds within the xy plane to be converged in the field direction, to attain the magnetization reversal. This state is shown in FIG. 1A. As shown in this figure, the magnetization vector rounds in the order of arrows 0 (initial state)xe2x86x921xe2x86x922xe2x86x923xe2x86x924xe2x86x925, to be finally converged in the xe2x88x92x direction by relaxation.
On the contrary, if xcex1 is significantly smaller than 1 and thereby the first term of the equation (1) becomes dominant, the change in magnetization vector with time, that is, dM/dt is usually perpendicular to the direction from M to H. Accordingly, the magnetization vector M undergoes precession rounding around the field vector H with an angle from the field vector H kept constant.
In the case of a magnetic substance in which xcex1 contributes to movement of a magnetization vector although the value of xcex1 is small, when a magnetic field in the xe2x88x92x direction to a magnetization vector directed in the + direction, the magnetization vector undergoes the precession rounding around the x-axis with an open angle from the x-axis gradually increased, and is finally relaxed to the field direction. A first half of a spiral locus of the termination of the magnetization vector is shown in FIG. 1B.
The magnetization reversal caused by a magnetic field directed in the direction reversed 180xc2x0 to the magnetization vector in the initial state is generally intermediate between the above-described magnetization reversal with an extremely large damping factor xcex1 and the magnetization reversal with an extremely small damping factor xcex1. The time required for magnetization reversal is important as a parameter determining the operational speed of a magnetic device. If the damping factor xcex1 is extremely large, the movement of the magnetization vector depicts a locus nearly along the shortest distance; however, the movement is slow and thereby the reversal time is long. On the contrary, if the damping factor a is significantly small, the movement of the magnetization vector is quick; however, it depicts a spiral locus and thereby the time required for the magnetization vector to be converged to the final state is long. The quickest magnetization reversal is obtained with the damping factor set at 1 (xcex1=1). Such a damping state allowing the quickest response is called xe2x80x9ca critical damping statexe2x80x9d.
For example, in the case of Permalloy (Ni"THgr"Fe alloy) often used for a magnetic functional device such as an MRAM, the critical damping appears when the size of the device is about 1 xcexcm, and accordingly, the design of most of MRAMs having the size of about 1 xcexcm, which have been extensively developed at present, is advantageous in making effective use of the material characteristic, that is, the critical damping of Permalloy. The damping, however, is nearly proportional to the square of the size of a magnetic device as described above, so that if a magnetic device has a fine structure, the degree of fineness of which is on the order of sub-micron, such a device causes a problem that the speed of magnetization reversal becomes slow because of the insufficient damping.
The quick switching of magnetization of a magnetic device using a magnetic substance, which has a fine-structure and thereby has an insufficient damping, is attained by the following drive method.
As shown in FIG. 1C, a magnetic field or an effective field equivalent thereto, which is derived by a magnetic anisotropy or exchange interaction, is applied in the direction (z-direction in the figure) perpendicular to the magnetization vector xe2x80x9c0xe2x80x9d in the initial state, which is directed in the +x direction. In this case, since it is assumed that the damping is small, the magnetization vector is not moved to the field direction but undergoes the precession around the z-axis.
To be more specific, as shown in FIG. 1C, the magnetization vector is turned nearly within the xy-plane in the order of the arrows 12345. On halfway of the precession motion, the drive force in the z-direction is cut off at the moment when the magnetization vector is nearly directed to the xe2x88x92x direction, that is, reaches the state shown by the arrow xe2x80x9c4xe2x80x9d in FIG. 1C. At this time, the magnetization remains in the xe2x88x92x direction, to be reversed from the initial state by 180xc2x0. The time required for this magnetization reversal is nearly equivalent to a half of one cycle of the precession motion. With this drive method, even if the damping factor xcex1 is significantly small, it is possible to realize magnetization reversal quicker than the magnetization reversal via the precession motion repeated by several times as shown in FIG. 1B.
Such a method for driving magnetization reversal shown in FIG. 1C is hereinafter referred to as xe2x80x9cswing-by switchingxe2x80x9d. This wording expresses a feature of the present invention in which a magnetization vector is moved toward a drive force but is moved toward a final state while passing by the drive force.
Results of numerical examination of such a swing-by switching will be described below.
The process of magnetization reversal of a magnetic substance performed by swing-by switching is numerically calculated on the basis of the equation (1), and the results thereof are shown in FIG. 2. An effective field used for calculation contains not only an external magnetic field but also effects of an uniaxial magnetic anisotropy and demagnetization field. A single magnetic domain Permalloy thin film is used as the magnetic substance. A saturation magnetization Ms is set at 800 emu/cm3. An easy axis of magnetization of the uniaxial induced magnetic anisotropy is set to correspond to the x-axis. An anisotropy field HK is set at 4 Oe. The damping factor xcex1 is set at 0.01. A magnetization vector in the initial state is set in the +x direction, and a magnetic field of 1 kOe is applied in the +z direction for a time of 0.2 ns. Under these conditions, the process of magnetization reversal performed by the swing-by switching is examined.
In FIG. 2, the abscissa indicates a time (ns), and the ordinate indicates an azimuth angle (xc2x0) representing the direction of the magnetization vector, which angle is measured within the xy-plane with respect to the +x direction. It should be noted that the magnetization vector has a component in the z direction; however, in the case of the thin film sample, the rise of the magnetization in the z direction perpendicular to the film surface is obstructed by the demagnetization field, and therefore, the component is negligible.
As shown in FIG. 2, the azimuth angle of the magnetization vector is linearly increased after application of the magnetic field, and after an elapse of 0.2 ns, the azimuth angle exceeds 160xc2x0. At this time, since the application of the magnetic field is stopped, the magnetization vector undergoes the anisotropic magnetic field and the demagnetization field. That is to say, since the direction of the effective field is changed from that during application of the external magnetic field, the axis of the precession motion is instantly changed, and thereby the rate of change of the azimuth angle becomes discontinuous. However, since the magnetization vector is already separated from the initial state by 90xc2x0 or more and is within a range of an attractive force toward an easy axis of magnetization directed in the xe2x88x92x direction, the magnetization vector is oscillatingly relaxed in the 180xc2x0 direction to be thus converged to the final state. It takes only 0.2 ns to drive the magnetization vector toward the final state.
A result of calculating the process of magnetization reversal of a comparative example, in which a magnetic field of 5 Oe is applied to a magnetization vector directed in the + direction in the initial state, is shown in FIG. 3. As shown in FIG. 3, it takes a lot of time for the magnetization vector to be separated from the +x direction.
The function of changing the direction of a magnetization vector by 90xc2x0 or 180xc2x0 is called a magnetization switching function. This function may be assembled with another function, to produce a magnetic device exhibiting various functions. For example, the composite of the magnetization switching function and a spin valve structure, in which writing is performed by the magnetization switching function and the magnetization state is read out by the spin valve, is applied to a memory, and further, since a current flowing in an output circuit can be controlled by the same configuration, such a composite structure can be applied to a switching device replaced from a transistor, and to a logic device by combination of the switching devices.
A general theory associated with the precession and relaxation of a turning magnetization vector has been reported by S. Chikazumi, Physics of ferromagnetism, John Wiley and Sons, Inc., 1964.
It has been already pointed out by a document (xe2x80x9cEngineering of Magnetic Thin Filmxe2x80x9d edited by Ryouta Sakurai, paragraph 4.2.2, Maruzen, 1977) and a paper cited in the document (D. O. Smith, J. Appl. Phys. 29, 264 (1958)) that the magnetization switching for a uniaxial anisotropic magnetic thin film becomes faster by adding a field component perpendicular to an easy axis of magnetization.
A paper recently published (R. L. Stamps, and B. Hillebrands, Appl. Phys. Lett. 75, 1143 (1999) has described that, upon reversal of a magnetization vector directed in an easy axis of magnetization by applying a magnetic field in the reversed direction to the magnetization vector, the rise of the magnetization reversal can be effectively accelerated by adding a small bias magnetic field in the direction perpendicular to the easy axis of magnetization. The content of this document is common to that of the above document by D. O. Smith.
In recent years, there has been reported an experiment performed by making a high speed pulse electron beam penetrate a perpendicular magnetization film, to generate a magnetic flux caused in the shape of concentric circle around the beam, and causing magnetization reversal by a combination of the easy axis of magnetization in the vertical direction and a magnetic field due to the magnetic flux thus generated within a plane of the film (C. H. Back, D. Weller, J. Heidmann, D. Mauri, D. Guarisco, E. L. Garwin, and H. C. Siegmann, Phys. Rev. Lett. 81, 3251 (1998)).
In this way, the effect of a magnetic field in the direction perpendicular to a magnetization vector exerted on magnetization reversal has been studied for a long time as a natural phenomenon.
However, the contents of the above-described documents, the paper by D. O. Smith, the handbook by Sakurai, and the paper by R. L. Stamps, and B. Hillebrands are characterized in that the main field component is opposed to the magnetization vector in the initial state, and the field component perpendicular to the magnetization vector is small and only functions as a supplementary field component. These documents do not teach even the possibility that the vertical or perpendicular field is used as a main drive force for driving the magnetization reversal like the present invention.
The above-described report by C. H. Back, et al. has experimentarily showed that magnetization reversal occurs by a pulse field perpendicular to the magnetization direction; however, they have made the experiment on a large scale by making an electron beam penetrate the magnetic thin film placed in vacuum, and have not described the application of the technique to practical information storage apparatuses such as a hard disk drive mainly used at present for magnetic recording, or a small-sized solid-state magnetic memory. Further, the arrangement disclosed in this document is limited to application of the magnetic field directed in the direction within the plane of the film to the perpendicular magnetization film.
To solve the above problems, according to a first embodiment of the present invention, there is provided a magnetization drive method including the step of: changing the direction of a magnetization vector of a magnetic substance by applying a drive force to the magnetic substance; wherein the drive force is applied in pulse to the magnetic substance in the direction nearly perpendicular to the magnetization vector of the magnetic substance in the initial state before the application of the drive force.
According to a second embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance; and drive force applying means for changing the direction of a magnetization vector of the information carrier, thereby processing binary or more information by magnetization directions of the information carrier; wherein the drive force is applied in pulse to the information carrier in the direction nearly perpendicular to the magnetization vector of the information carrier in the initial state before the application of the drive force.
In the above second embodiment, the information carrier and the drive force applying means may be integrally assembled on a substrate, to function as a solid-state device. An effective magnetic field derived from a magnetic anisotropy or an effective magnetic field derived from an exchange interaction applied from a different magnetic substrate coupled to the information carrier may be used as the drive force. A magnetic substance having a uniaxial magnetic anisotropy may be used as the magnetic substance constituting the information carrier, and binary information be processed by normal and reversal magnetization directions along an easy axis of magnetization of the magnetic substance; and a drive force for reversal of magnetization be applied in the direction nearly perpendicular to the easy axis of magnetization of the information carrier.
According to a third embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is obtained by generating a magnetic anisotropy having an easy axis of magnetization directed in the direction nearly perpendicular to the easy axis of magnetization of the information carrier in the static state.
In the above third embodiment, the magnetic anisotropy functioning as the drive force may be a stress-induced magnetic anisotropy. The information carrier may be formed by a magnetic thin film having a magnetic anisotropy changed sensitively to a strain (or stress), the magnetic thin film being stacked to a piezoelectric layer; and a voltage be applied in the thickness direction of the piezoelectric layer, to generate the stress-induced magnetic anisotropy. The information carrier may be formed by a magnetic thin film having a magnetic anisotropy changed sensitively to a strain, the magnetic thin film being stacked to a strain imparting layer; and a uniaxial strain be imparted to the strain imparting layer in a specific direction within a plane of the strain imparting layer, to generate the stress-induced magnetic anisotropy having an easy axis of magnetization directed in the specific direction. The information carrier may be formed by a perpendicular magnetization film having the easy axis of magnetization in the static state which is directed in the direction perpendicular to a plane of the perpendicular magnetization film; and the drive force be applied in the direction nearly parallel to the plane of the information carrier. In addition, the strain used for generating a stress-induced magnetic anisotropy is not limited to an uniaxial strain but may be a strain being isotropic in a plane.
According to a fourth embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is generated by an exchange interaction applied from a different magnetic substance provided adjacently to the information carrier.
In the above fourth embodiment, the information carrier may be formed by a thin film or a flat magnetic substance having the easy axis of magnetization in the static state within a plane of the magnetic substance; and the drive force be applied in the direction nearly perpendicular to the plane of the information carrier. A magnetic layer to be controlled, which constitutes the information carrier, may be stacked on a fixed magnetization layer via an intermediate layer; and the strength of an exchange interaction between the magnetic layer to be controlled and the fixed magnetization layer be changed by the effect of the intermediate layer. The information carrier may be formed by a perpendicular magnetization film having the easy axis of magnetization in the static state which is directed in the direction perpendicular to a plane of the perpendicular magnetization film; and the drive force be applied in the direction nearly parallel to the plane of the information carrier. A magnetic layer to be controlled, which is formed by the perpendicular magnetization film constituting the information carrier, may be stacked on a fixed magnetization layer via a connection control layer; and the strength of an exchange interaction between the magnetic layer to be controlled and the fixed magnetization layer be changed by the effect of the connection control layer.
According to a fifth embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is derived from a magnetic field applied to the information carrier from external.
According to a sixth embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the information carrier has a composite structure in which two or more magnetic substance layers are stacked to each other.
In the above sixth embodiment, the two or more magnetic substance layers constituting the information carrier may include a magnetic substance layer having an easy axis of magnetization directed in the direction nearly perpendicular to a plane of the magnetic layer. The two or more magnetic substance layers constituting the information carrier may be composed of an anisotropy imparting layer and a magnetic thin film having a magnetic anisotropy changed sensitively to a strain. The information carrier may have a structure in which a strain imparting layer, the magnetic thin film, and the anisotropy imparting layer are sequentially stacked to each other. The information carrier may have a structure in which the magnetic thin film, the anisotropy imparting layer, a connection control layer, and a fixed magnetization layer are sequentially stacked to each other. The information carrier may have a structure in which a strain imparting layer, the magnetic thin film, the anisotropy imparting layer, a connection control layer, and a fixed magnetization layer are sequentially stacked to each other.
According to a seventh embodiment, there is provided a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the magnetization vector in the static state of the information carrier is tilted by a specific angle with respect to the easy axis of magnetization in the static state.
According to an eighth embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance; and drive force applying means for changing the direction of a magnetization vector of the information carrier, thereby processing binary or more information by magnetization directions of the information carrier; wherein the drive force is applied in pulse to the information carrier in the direction nearly perpendicular to the magnetization vector of the information carrier in the initial state before the application of the drive force; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
According to a ninth embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is obtained by generating a magnetic anisotropy having an easy axis of magnetization directed in the direction nearly perpendicular to the easy axis of magnetization of the information carrier in the static state; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
According to a tenth embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is generated by an exchange interaction applied from a different magnetic substance provided adjacently to the information carrier; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
According to an eleventh embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the drive force is derived from a magnetic field applied to the information carrier from external; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
According to a twelfth embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the information carrier has a composite structure in which two or more magnetic substance layers are stacked to each other; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
According to a thirteenth embodiment, there is provided a magnetic apparatus including: (A) a magnetic functional device including: an information carrier formed by a magnetic substance having a uniaxial magnetic anisotropy; and drive force applying means for applying a drive force, which is used for reversing the direction of a magnetization vector of the information carrier, in pulse to the information carrier in the direction nearly perpendicular to an easy axis of magnetization of the information carrier in a static state, thereby processing binary information by magnetization directions of the information carrier; wherein the magnetization vector in the static state of the information carrier is tilted by a specific angle with respect to the easy axis of magnetization in the static state; and (B) means for reading out a magnetization direction of the information carrier of the magnetic function device by a Hall effect or magneto-resistance effect.
The examples of the above-described magnetic apparatuses may include various kinds of functional apparatuses such as a magnetic recording apparatus, a current switching device, a voltage switching device, a logic device, and a magnetic base type computer.
According to the present invention, the size of a magnetic substance or an information carrier of the magnetic functional device of the present invention may be determined as needed, and in particular, if a fine-structure of the magnetic functional device is intended to be made finer, the length of the maximum side of the device may be on the order of sub-micron, more specifically, be selected in a range of 500 nm or less.
The magnetic functional device of the present invention can be applied not only to a magnetic storage apparatus but to various apparatuses making use of the magnetization switching, for example, a current control device.
According to the present invention configured as described above, since the direction of a magnetization vector of a magnetic substance or information carrier of the magnetic functional device is reversed by applying, in pulse, a drive force derived from a magnetic anisotropy or exchange interaction in the direction nearly perpendicular to an easy axis of magnetization of the magnetic substance or information carrier in the static state, that is, the swing-by switching operation is performed, even if the size of the magnetic substance or information carrier, particularly the size of the maximum side thereof is made finer on the order of sub-micron and further deep sub-micron, a significantly displacement of the magnetization starts directly after application of the drive force without being affected by an insufficient damping to the magnetization vector, with a result that it is possible to reverse the direction of the magnetization vector without depicting an useless locus, and hence to carry out the swing-by switching operation at a high speed.